DC Voltage and Current Interview Questions 

The power-delay product for a CMOS gate is 0.1 pJ at a frequency of 1 GHz, for a power supply voltage (VDD) of 1 V, and for a capacitive load of 1 pF. Its average propagation delay is measured to be 100 ps. Assume that the DC or static power dissipation of the CMOS gate is zero.

a)Determine the dynamic power dissipation in mW of the CMOS gate for VDD = 1 V at 1GHz.

b) Determine the average power supply current in mA of the CMOS gate for VDD = 1 V at 1GHz.

c) Determine the dynamic power dissipation in mW of the CMOS gate for VDD = 1 V at 100MHz.

i want to make this DC motor speed control:
(only the last page matters)
http://kitsrus.com/pdf/k166.pdf
but i need huge amounts of more power..

this circuit is limited to 49amps by the two TRFz44 N-channel mosfets.
and 32v by the LM324 OP-amp

Im halfway through an EE degree, but we havent touched transisters yet.

CURRENT:
Can I just hook more of the same mosfets in parallel to handle more Amps? IF NOT: when i lookup this irfz44 on digi-key, it lists 100 different ones with different specs.. but the circuit does not specify.. would any work?

VOLTAGE:
whats an op-amp that handles more V that would work the same?
would any quad op-amp, 14pin work??

i need this circuit to handle these
.........min-max values
volts.. 36v-150v
amps 100A-500A
watts- as much as possible!!!

im guessing if you say it would work, hooking many mosfets in parrallel would be the solution... so then the only issue is the op-amp needs to be a higher voltage one.

I'm building a circuit with a H-bridge driver.

It works fine using PNP and NPN transistors, but draws more current than I'd like (when the NPNs are off, their base current gets diverted to ground, so it's still flowing; and this needs to be several mA because of the low hFE of the power trannies). So I thought of changing to use FETs; but then I am going to need a higher voltage supply than I've already got, to drive the gates of the top-side FETs.

Does anyone know of a moderately-easy way of stepping up a 12V DC supply (lead acid battery) to get my gate drive? It doesn't have to be able to supply a lot of current since it's only turning on FETs (probably IRF740, since this is what Maplin Electronics in Stoke sell).

Bonus points if all parts can be scored from Maplin!

15. A circuit contains four resistors connected in series. R1 is 100 O, R2 is 200 O, R3 is 240 O, and R4 is
600 O. What is the total circuit resistance?
A. 1,200 O C. 600 O
B. 1,140 O D. 80 O17. What is the power dissipated by R2 in the circuit shown in the figure in Question 16?
A. 5 W C. 16 W
B. 12 W D. 33.3 W 18. Which one of the following voltages should never be measured directly with a VOM?
A. 100 V C. 800 V
B. 500 V D. 1,200 V 19. Which of the following is the correct formula for finding power in a DC circuit?
A. P = IR C. P = ER
B. P = I2R D. P = E2I 20. What is the voltage in a circuit with a resistance of 100 O and a current of 0.04 A?
A. 4 V C. 10 V
B. 8 V D. 40 V

I am trying to power an electromagnetic coil with a mains operated step down PSU. The voltage i want to supply the coil with is 6V DC at 1.25A. The only trouble with this is, if i connect the supply directly to the coil, the PSU's protection circuit trips. I assume this is because the coil is drawing to much current, any ideas on how to rectify this problem? coil details:
coil resistance 2.8 Ohm

NB: it has been recommended that a diode be placed on the (+) positive lead to the coil to protect the PSU, but i do not think this will resolve the issue of the PSU tripping when supplying power

how would you draw a circuit with the instructions provided? I am so confused! we have this really laid back teacher who doesn't really explain to us anything at all

anyway
don't quite understand how to draw a circuit diagram. Here are the instructions:
1) A DC power supply is used to operate a motor. The power supply is connected to a motor and a variable resistor in parallel with each other. The circuit is then completed with switch with a light bulb. An ammeter measures the current through the motor and a voltmeter meaures the voltage at the power supply.

Can you explain to me how to DRAW a circuit diagram NOT MAKE it.

2)What's resistance? how do you solve for it in a mathematial problem?

Thanks :)

To save cost, i want to use a 24V 40Ah power supply to power 2 dc permanant magnet motor,one is 24V 30A and one is 12V 10A. Using a converter to change the voltage from 24 to 12V, i notice that basically the power will not change from input to output, then i guess the current output would be large. Is it okay to provide such a large current input (in this case 40Ah,when the output current only need 10A)?

If the reverse bias exceeds the avalanche voltage in a P-N junction
(a) the junction will be destroyed
(b) the junction will insulate; no current will flow
(c) the junction will conduct current
(d) the junction will be destroyed AND no current will flow

In a full-wave rectifier, the unfiltered output voltage
(a) is the same frequency as the source
(b) is twice the frequency of the source
(c) is half the frequency of the source
(d) is pure DC and does not depend on the frequency of the source.

A bipolar transistor has
(a) three P-N junctions
(b) three semiconductor layers
(c) two N-type layers around a P-type layer
(d) a low avalanche voltage

A bipolar junction transistor acts like the following dependent source:
(a) VCVS
(b) CCCS
(c) CCVS
(d) VCCS

Which of the following is not an advantage of semiconductor devices over vacuum
tubes?
(a) smaller size
(b) lower working voltage
(c) lighter weight
(d) ability to withstand high voltage spikes

The purpose of doping is to
(a) make the charge carriers move faster
(b) cause holes to flow
(c) give a semiconductor material specific properties
(d) protect devices from damage in case of transients

I don't quite understand how to draw a circuit diagram. Here are the instructions:
1) A DC power supply is used to operate a motor. The power supply is connected to a motor and a variable resistor in parallel with each other. The circuit is then completed with switch with a light bulb. An ammeter measures the current through the motor and a voltmeter meaures the voltage at the power supply.

can you explain to me how you'd draw this kind of circuit- i really need to know for my exam!

25. What does the acronym DC stand for?
a. Direct Circuits
c. Direct Current
d. Dynamic Current

26. What does the acronym VGA stand for?
a. Voltage Graphic Adapter
b. Video Graphic Array
c. Volatile Graphic Array
d. Video Ground Array

34. Name at least 4 output peripheral devices.
35. Name at least 4 storage devices.
36. Name at least 4 input peripheral devices
37 What is the size of a regular 1.44 mb floppy drive?
a. 3 1/4"
b. 3 1/2"
c. 5 1/4"
d, 3 1/8"

38. What type of connector does a NIC card have?
a. Phone Jack
b. RJ13
c. RJ11
d. RJ45

41. Which one is a Mouse connector?
a. UART connector
b. BNC connector
c. PS/2 connector
d. LPT connector

42. What size bus does the last version of ISA slot handle?
a. 8 bit
b. 16 bit
c. 32 bit
d. 64 bit

47. What are the IRQ 5 used for?
a. Serial port
b. sound card
c. usb port

49. What is the IRQ 1 used for?
a. Parallel Ports
b. Serial Ports
c. Keyboard
d. Monitor

I want to check and see if I understand all of this correctly, so I'll list what I am thinking happens and you can correct me if I'm wrong, Ok?
I am talking about a very basic inductor in a very basic DC circuit, I am only wanting to understand the operation of an inductor in a circuit.

1. When the cirucit is first energized the coil acts like a resistor, it drops the maximum amount of voltage ( the amount of the source) which declines rapidly as the field builds. The voltage it drops is opposite to the increase in polarity only, equal in value.So it is exhibiting decreasing resistance to current flow in this charging state.

2 As current is decreased, the coil releases its energy by dropping a voltage of the same polarity to attempt and maintain the current's prior state. It is acting as a source in this state, but increasing its resistance to the change as its field deteriorates.
3. Steady state of current....NOT Sure?

Hi

If we have dc hysteresis loop from the manufacturer , how to plot the exciation current in time domain for 50 Hz supply voltage

please consider this

Q1

Find the peak current through a 0.04H inductor when the voltage across it is

v(t) = 5sin(1800t) V

Ans = 69.4 mA again working out is needed

Q2 Find the inductive reactance of

a. 0.06H inductor at DC
b. 1.5H inductor when the voltage across it is 65sin(320t)mV

Ans

a.0
b.480O

Q3

Find the peak current through a 0.01µF capacitor when the voltage across it is

v(t) = 169sin(377t) µV

Ans = 0.637A, working out please

Hope you guys can help me out, thanks!

I have got a UPS Powerware 9110, 1000Va, pf 0.7, 700W with charging capacity of 36 Volt DC at 30 Amp DC.

I connected three new 12 Volts 45Ah Deep Cycled Flooded Batteries in series.

The Charging Capacity is very low i-e 1.5 Amps.

I want to have an additional external Charger. Please note that the internal charger with open circuit gives 41.1 DC Volts. I've planned to attach an external charger in pararell to the internal to increase the current in Amps (say 3 or 4 more amps) and of course the charger should be smart enough to proctect my batteries as well.

Please advice if it is safe to have another charger with my unit, if YES then please advise the correct model and its price.
Also I have a confusion that when UPS's internal charger shows 41.1 Volts then what will happen if I install 2nd charger of some different Voltage like exact 36 or 39 volts. Wouldn't the current moves towards the lower voltage instead of just charging the batteries?

You have a 10 k? resistor that is rated to withstand a maximum power of 4 W. If you connect this resistor within a DC circuit, what is the highest voltage that can be safely applied across this resistor, and what is the corresponding maximum current that can flow through the resistor?

im new to physics, so could u explain how u got the answer. its probably a simple question. but i suck at physics.